The present invention relates to a longitudinal multi-component frame element, for example to be used in forming a frame for a window or door. More particularly, the present invention is directed to such a frame element of the type including at least one longitudinal member, for example formed of a plastic material, wood or metal, for example aluminum, in various forms such as sheet metal or extruded metal, with a rigid plastic core component connected to such member in a positive, rigid or non-positive manner.
Furthermore, the present invention is directed to a process and apparatus for the production of such a longitudinal multi-component frame element.
Frame elements of this general type normally are produced in lengths of up to approximately six meters. At least one longitudinal member, for example two such longitudinal members to form opposite outer side portions of the frame element, and formed, for example, of aluminum are positioned within a longitudinal mold. There then is injected into the mold to fill the remaining cavity thereof a foamable and curable material such as polyurethane. This material cures to form a rigid plastic component connected to the longitudinal member or members. Such a frame element is disclosed in German DE-PS 32 42 909.
It is a prerequisite for the use of this type of frame element that the frame element not be warped in the longitudinal and transverse directions, i.e. have substantially perfect longitudinal dimensions. However, this is difficult to achieve in practice, particularly when the frame element and the components thereof are not symmetrical when viewed in transverse cross section. Particularly, during foaming and curing, the rigid plastic foam becomes connected positively and non-positively to the inner surfaces of the longitudinal members, for example extruded aluminum members. Furthermore, outer walls of the plastic member not adjacent the aluminum members cure more densely than the inner core or center zone of the rigid plastic component. During foaming temperatures ranging from 120.degree. C. to 180.degree. C. are produced in the center core zone, depending on the course of the involved reaction and the relative dimensions involved. When cooling to room temperature, internal stresses are generated within the frame element. These stresses result from the factors of temperature differential, reaction loss of the plastic material, and varying coefficients of expansion of the metal members, the outer more dense plastic zones and the inner or core less dense plastic zone. Accordingly, when the frame element is removed from the mold, particularly when the frame element has an asymmetrical cross section, such internal stresses will result in warping of the frame element. That is, when the axes of masses of the various components, taken in the longitudinal direction, do not coincide, then warping of the frame element will occur. This problem also results when the longitudinal side members of the frame element are formed of a material other than metal, for example wood or plastic.
In the manufacture of this type of frame element, it is customary to first determine the functional design features of the frame element, i.e. the dimensions and transverse configuration thereof. Normally the longitudinal axes of mass of the plastic material in the core zone and/or in the outer zones will deviate from the longitudinal axes of mass of the metal (or other material) side members. To avoid warping of the frame element, it has been necessary in the past to attempt to make such longitudinal axes coincident. This is normally done by extensive mathematical and design simulation exercises by computer, for example varying wall thicknesses of the outer longitudinal members or by altering shapes thereof. When coincidence of the longitudinal axes has been achieved mathematically, then the resulting data are converted into actual production. Thus, to achieve a non-warping property of a particular frame element it may be necessary to use a thicker wall dimension or modify the shape of at least one of the outer wall members. Since such outer members normally are formed of a more expensive material, such as extruded aluminum, wood or plastic, the need to use additional such material to achieve coincidence of the axes increases the cost of the finished product. Additionally of course, such computerized mathematical simulation itself is expensive.
Such known techniques suffer from certain additional inherent disadvantages. Thus, the equilibrium between the longitudinal axes of masses of the various components, although once determined in the above manner, can be imbalanced or destroyed by production deviations of the wall thicknesses of the outer members during production thereof, thereby inevitably again resulting in warping of the finished product. Such deviations can occur due to wear of the various parts employed in tools for manufacture of the outer members, for example wear of extrusion dies in the case of extruded aluminum members.
Furthermore, in the above conventional arrangement it is not possible to replace one or more of the outer members with a different material, for example other metals such as copper or other materials such as wood or plastic, without disturbing the equilibrium of coincidence of the axes thereof. That is, when there becomes a change in the materials, there also will be changes of coefficients of expansion. Similarly, any changes in wall thickness or configuration of the outer members similarly will result in lack of coincidence of the axes. Yet further, it is not possible in such known system to employ outer members formed by conventional rolling techniques, due to the expense in sufficiently accurately controlling wall thicknesses thereof to ensure coincidence of the axes. Thus, changes of wall thickness of the outer members can, as indicated above, shift the axes out of coincidence.